Forecast Discussions mentioning any of "ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 05/25/20

Area Forecast Discussion

National Weather Service Los Angeles/Oxnard CA

 854 PM PDT Sun May 24 2020

.SYNOPSIS...24/732 PM.

Temperatures will warm notably through midweek with many interior
locations in the 90s by Wednesday and a few sites reaching triple
digits. The heat will diminish slightly on Thursday then more
rapidly into the weekend. Some overnight and morning coastal low
clouds and fog will continue through midweek.

&&

.SHORT TERM (SUN-WED)...24/853 PM.

Upper level ridge started to build across the region today and
will continue to strengthen the next couple of days. The rising
heights combined with a light offshore wind influence across
interior areas resulted in substantial warming today for
the valleys, mountains, and deserts. A few of the hot spots
today included Paso Robles at 94 degrees and Woodland Hills
at 90 degrees. Current marine layer depth is around 1100 feet
across the LA basin according to latest ACARS data, and should
continue to shrink tomorrow. Current satellite imagery showing
low clouds and fog still well off the coast. With a weak
eddy circulation, thinking that most of the low clouds and
fog will be confined to the LA county coast overnight into
Monday morning.

Extended period of hot and dry conditions will occur
Monday through Thursday, leading to potential heat impacts
across the region. A slightly stronger offshore wind push
on Monday morning is expected to bring a rapid warm-up
to most inland areas. Most inland areas are expected to climb
well into the 90s on Monday, with a few of the hot spots (like
Paso Robles and Woodland Hills) approaching 100 degrees. In
addition, a light offshore wind influence Monday morning combined
with a rapidly shrinking marine layer will also lead to
significant warming across the Central Coast, where a heat
advisory has been issued. The hottest temperatures for the Central
Coast will mainly be 5-10 miles away from the coast as well as
foothill areas, which could see temperatures locally exceeding 90
degrees.

The northeast winds are mainly going to be confined to the
mountains, deserts, and interior valleys, as well as portions of
the Central Coast. Most of these areas could see offshore winds
gusting between 15 and 30 mph in the morning and early afternoon,
with local gusts as high as 35 mph in the LA county mountains.

The extended period of hot temperatures and low humidities
will bring an increased threat of grass fires as fine fuels
continue to dry rapidly.

*** From previous discussion ***

On Tuesday northeast flow weakens which should allow Central Coast
areas to cool slightly. However, the ridge aloft will strengthen
and shrink the inversion even more, down to just a few hundred
feet. Will likely still see some dense fog at the beaches and
5-10 miles inland as gradients start to shift onshore but beyond
that it will get hot fast with temps approaching triple digits in
the valleys and near 90 for interior parts of the coastal zones.
Overnight low temps will be tricky but an important factor in
determining heat risk as cooler temps would provide some relief.
The lack of wind and moisture should allow for decent radiational
cooling at lower elevations but a lot will depend on where the
inversion sets up. Hills and mountains will likely stay around 70
much of the night so it`s a close call on a heat advisory. At
current forecast temperatures it`s a very marginal heat advisory
event for the valleys. Also adding to the uncertainty is the
difference in model gradients as the GFS maintains an 8-9mb
onshore flow (LAX-DAG) while the EC remains much weaker between
2-4mb. Will defer on the heat advisory decision though high
confidence it will not be needed for coastal zones.

Wednesday not looking much different from Tuesday, though probably
starting off a few degrees warmer. With increasing onshore
gradients coast and some coastal valleys may drop a couple degrees
from Tuesday but farther inland areas will be a few degrees warmer.

.LONG TERM (THU-SUN)...24/216 PM.

Models have more or less maintained their respective trends for
later in the week with the GFS faster at shifting the Omega
blocking pattern to the east as and upper low approaches from the
southwest. In any case it doesn`t look like there will be much
impact on temperatures Thursday, though slightly warmer in the
Antelope Valley and other far interior areas. Both models do show
onshore gradients continuing to increase so coastal areas may shed
a couple degrees from Wednesday`s highs with some patchy marine
layer clouds and dense fog but still well above normal.

As the low gets closer Friday/Saturday the ridge will move farther
east and allow the coastal marine inversion to deepen and push the
cooler air inland. Not super confident temps will drop as much as
models are showing on Friday but more confidence in temps
returning to normal levels next weekend.

&&

.AVIATION...25/0253Z.

At 2350z at KLAX... The marine inversion was around 1100 feet.
The top of the inversion was around 3200 feet with a temperature
of 21 degrees Celsius.

Overall... Moderate to high confidence in the current TAFs.
VFR conditions expected across much of the forecast area through
the forecast period, except IFR/LIFR conditions likely at KLAX
and KLGB 11z-16z, with a 40 percent chance of IFR/LIFR cigs
at KSMO. There is also a 40 percent chance of LIFR/VLIFR
conditions for KSMX overnight.

KLAX... Moderate to high confidence in the current TAF. Mostly
VFR conditions at LAX, except IFR/LIFR cigs likely between
11z-16z, with lingering MVFR vsbys in haze lingering until around
18z. There will not be any east winds greater than 8 kts during
the forecast period.

KBUR... High confidence in the current TAF. VFR conditions will
prevail throughout the forecast period.

&&

.MARINE...24/748 PM.

Across the outer waters... Winds will be elevated and gusty to Small
Craft Advisory (SCA) level tonight, then will diminish and
conditions will remain below SCA levels Monday through Friday.

Across the nearshore waters of the Central Coast... Wind gusts will
be elevated and gusty tonight, then will diminish and conditions
will remain below SCA levels through Friday.

Across the inner waters south of Point Conception... Winds will
be elevated and gusty to SCA level tonight from Point Conception
to Point Mugu with the strongest winds across the western portion
of the Santa Barbara Channel. The winds will diminish early on
Monday and conditions will be less than SCA levels through Friday.

There will be patchy dense fog with visibility under one mile
overnight and in the morning hours along the Central Coast and
along the Orange and Los Angeles County coastline.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...Heat Advisory in effect from 11 AM to 7 PM PDT Monday for
      zones 34>36. (See LAXNPWLOX).
     Excessive Heat Warning in effect from noon Tuesday to 7 PM
      PDT Thursday for zone 59. (See LAXNPWLOX).
PZ...Small Craft Advisory in effect until 3 AM PDT Monday for
      zones 650-670-673-676. (See LAXMWWLOX).

&&

.HAZARD POTENTIAL OUTLOOK (WED-SUN).

Hot temperatures are expected Wednesday and Thursday, especially
away from the coast, which may lead to an increased risk for heat
related illnesses for sensitive populations. Possible dense fog
along the the L.A. County coast Wednesday and Thursday mornings
could create driving hazards.

&&

$$

PUBLIC...Gomberg/MW
AVIATION...Gomberg
MARINE...Kj
SYNOPSIS...Kj

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